The present invention relates to a pneumatic tire having an improved carcass structure capable of improving steering performance without increasing the tire weight, and also relates to a method of making the same.
In general, a pneumatic tire is provided with at least one carcass ply. Further, in order to reinforce the tread portion, a belt composed of cords arranged at different angles from the carcass cord angle is disposed. Furthermore, to reinforce the bead portion and sidewall lower portion, a hard rubber bead apex and a bead reinforcing cord layer having a different cord angle from the carcass cord angle is disposed. Therefore, due to the different cord angles, an additional carcass ply can not be substituted for such a belt and bead reinforcing layer.
On the other hand, recent high performance motorcars require a high performance tire in which steering performance is improved but the tire weight is not increased.
If an additional carcass ply is disposed, the lateral stiffness of the tire is increased and the steering performance can be improved. However, such an additional carcass ply is redundant in the tread portion and bead portion and only increases the tire weight. If the additional carcass ply is not disposed, the tire shoulder portion or sidewall upper portion becomes relatively weak. Therefore, if a reinforcing cord layer is disposed partially in the shoulder portion, the edges of the layer are liable to separate since the bending deformation of the shoulder portion is greatest.